Parasitology is a science that studies the phenomenon of parasitism. The main task of such science is to study the relationship between parasites and hosts, their influence on each other, which also depends on environmental factors.
Due to the increase in population migration (the development of tourism, due to the increase in the number of people arriving from different countries), the role of the science of parasitism in the health care of the modern world has increased several times. Let's then look at what parasites can live in the human body and what symptoms can arise from various infections.
The number of people with immunodeficiency has increased, including patients with HIV infection, as well as due to advances in medicine related to the use of chemotherapy and developing transplantology.
All this leads to the fact that most diseases (infestations) caused by parasites, which usually occur without complications or without any symptoms, can be fatal in people with a weakened immune system.
The response to the introduction of parasitic organisms in such patients differs significantly from the usual response, which leads to the appearance of acute, atypical forms of the disease.
Also, the activity of the human population provokes global changes in climatic conditions and the natural landscape, which leads to the spread of infection vectors from endemic areas to other areas and regions.
Medical parasitology is divided into several sections depending on the belonging of the parasitic organisms to different groups: protozoan parasites, helminth parasites, parasitic arthropods, etc. Thus science is divided into:
- Medical protozoology (study of parasitic protozoa, symptoms and treatment of protozoa);
- Medical helminthology (study of parasitic worms, symptoms and treatment of helminth infections);
- Parasitic entomology (the study of parasitic arthropods).
Relationships between organisms
Parasitism is a special way of relationship between organisms of different species, in which one of them (the parasite) uses the other (the host) as a place of permanent or temporary life, as well as a source of food.
The parasite does not immediately kill its host; first it must be fed repeatedly. In the course of evolution, parasites have developed special mechanisms of interaction with their hosts, which ensure the vital activity of all types of parasites.
External natural conditions affect the parasites not directly, but indirectly, through the hosts.
The phenomenon of parasitism is quite widespread on the planet. Parasites can belong to any systematic group of all kingdoms of organisms. Any type of organism, with the exception of viruses, can become a "home" for parasites.
In this case, the parasitic individuals themselves become hosts for parasites from other classification groups of animals.
Parasitocenosis is the total number of absolutely all parasitic organisms that simultaneously live in the host. The causative agent of the disease are parasitic organisms specific to different types of hosts.
Parasites living inside their host not only feed but also cause various diseases that can lead to the death of the affected person. This phenomenon is called pathogenicity.
Parasites in the human body have a negative impact on it through several mechanisms:
- Damage to cells and tissues;
- Impact on immune defense mechanisms and the production of antibodies by the host;
- Sensitization of the host organism (hypersensitivity);
- Toxic action of the metabolic products of the parasites.
The developmental cycle of the parasite is the total number of morphological phases of development of the organism, as well as an indication of the habitat of each phase, the route of infection and transmission.
For example, the following phases are distinguished in the development of parasitic worms: invasive phase - entry into the body of the host; larval stage; phase of an adult, sexually mature individual.
Invasive diseases (infestations) are diseases caused by parasitic organisms. Invasive human diseases are divided into protozoal (they are caused by protozoa), helminthiasis (parasitic worms) and diseases caused by arthropod parasitism.
Signs of parasites in the human body are so diverse that it makes no sense to consider them in general. Therefore, we will look at the symptoms of the main protozoa, helminthiasis and infestations caused by other animal organisms.
Due to the need to adhere to a parasitic lifestyle, three types of parasitism are distinguished:
- False parasitism. The accidental introduction of a free-living individual into the host which may be viable for some time and which is capable of disrupting the normal processes of its life. False parasites are soon released into the environment (e. g. in faeces) or die after a short period of time. False parasitism is inherent in some leeches that accidentally fall into the nasal cavity of people, where they live and cause bleeding, mites and their eggs that fall into the stomach and are then excreted with feces, and some amoebas.
- Facultative parasitism is the ability of organisms to live both with and without a host. The viability of the parasite lasts longer than in the first case. This type is characteristic of fly larvae that are capable of developing outside a living organism and upon accidental entry into it (causing myiasis).
- True parasitism. This type of worming includes helminths, fleas, lice, etc.
| In relation to the body of the host | |
|---|---|
| Ectoparasites | They live on the surface of the skin, feeding on blood cells and the upper layers of the skin. |
| Endoparasites | They live in the tissues, cells and cavities of their hosts. They can be located in only one of the organs, but are able to move to the relatives, causing their damage as well |
| According to the duration of the contact | |
| A temporary parasite | Most often they are ectoparasites, their contact is usually short-lived |
| A stationary parasite | For such parasites, hosts are also a kind of "home". This method of parasitic lifestyle is divided into two types: intermittent (the parasite spends part of the time in the host) and permanent |
| By specifics | |
| Polyspecific | Able to change different types of hosts, as they feed on blood, epidermis and other tissues inherent in many types of living things |
| Monospecific | Able to parasitize only certain species (species) of hosts |
The concept of the owner
The host is a living organism that the parasite uses as a source of nutrients and a place to live. Most parasite individuals can switch hosts, which is due to the presence of several stages during the life of the parasite.
The definitive host (otherwise the primary, definitive, last) is an organism in which the parasite lives in the adult phase and can reproduce sexually.
An intermediate host is a host in which the larval stage of the parasite lives, or a stage that reproduces only asexually.
Reservoir host - within which the parasite is viable, increases in number, but does not mature further.
Parasitic diseases can be anthroponoses (disease sources and hosts are humans), anthropozoonoses (sources and hosts are both humans and animals), and zoonoses (sources and hosts are animals).
Many infections are called natural focal infections when pathogens move between wild animals in a certain area.
Methods for the diagnosis of parasitic infections
You cannot get rid of "parasites in the body" with the help of a "magic pill" or folk remedies, you can do even more harm to yourself. First, you need to find out what kind of infestation a person has. Macroscopic, microscopic and immunological methods are used for the diagnosis of invasive diseases.
Macroscopic techniques allow infectious agents to be identified on external surfaces or in the faeces of an affected person.
Microscopic methods also allow parasites to be identified in blood smears, tissue fluids, muscle tissue biopsies, as well as in sputum, feces, gastric and duodenal contents.
Parasitological studies use optical and electron microscopy methods using light and electron microscopes. Here, the diagnosis is primarily based on a thorough knowledge of the morphological structures of infectious agents, methods of preparation, fixation and staining of smear preparations.
Microscopy results depend on the selection of pathological materials, their nature, the time of collection from the onset of symptoms and the period of study from the moment of obtaining the material.
Immunological diagnostic methods include serological and allergic reactions. Serological tests are used to:
- To establish the type of organisms, toxins, antigens with the help of immune diagnostic sera;
- To determine the nature of antibodies in blood serum using diagnostic antigens.
The main serological reactions are reactions of agglutination, precipitation, lysis, binding of complement, neutralization, etc. Methods for using labeled antibodies are also known: immunofluorescence reactions, enzyme-linked immunosorbent assay, immunoblotting, radioimmunoassay.
Nucleic acid hybridization and polymerase chain reaction methods have found wide application in diagnostics.
Issues of prevention and anti-epidemic measures
Preventive measures for all parasitic diseases can be summarized as follows:
- It is necessary to protect the soil and water sources from contamination with human and animal excrement.
- There is a need to improve settlements and toilets.
- It is necessary to carry out sanitary supervision on the territories and water supply of the settlements, as well as on the production, transportation and sale of food products.
- It is important to carry out veterinary and sanitary supervision in slaughterhouses, meat processing plants, markets and livestock farms.
- It is necessary to identify and treat the carriers of infections.
- It is necessary to protect people from damage by arthropods and to promote knowledge about personal prevention of parasitic diseases.
Anti-epidemic measures include active detection of infected people and carriers, registration and treatment of the infected, hospitalization and, if necessary, medical examination, neutralization or destruction of the sources of infection. Personal prevention is of great importance: hygienic measures, annual medical examination, proper preparation for tourist trips, solving the issue of chemoprophylaxis.
Chemoprophylaxis, i. e. the application of anthelmintic drugs in risk groups and endemic areas 1 or 2 times a year, was developed by the WHO for disadvantaged and developing countries.
General properties of protozoa
Protozoa are unicellular organisms that have a nucleus (eukaryotes).
The size is no more than one millimeter, they are found everywhere and in all corners of the planet. Parasitic forms of protozoa are also divided into ectoparasites and endoparasites.
Characteristics of protozoa:
- The body is made up of a single cell that performs the function of both the cell and the organism as a whole. The shape of the body can be diverse: variable, elongated or spindle-shaped.
- Some protozoa are covered only by a cell membrane, while others have an elastic membrane called a pellicle.
- The cell cytoplasm is divided into: outer dense (ectoplasm) and inner (endoplasm). The cytoplasm may contain one or more nuclei.
- Nutrients enter in different ways: by pinocytosis (absorption), phagocytosis (active feeding), osmosis (absorption of substances due to a difference in concentration), active passage through the membrane.
- Gas exchange takes place throughout the cell due to the osmotic component. Waste products are also released from the entire cell surface and using digestive vacuoles.
- Unicellular organisms reproduce both sexually and asexually.
- Unicellular organisms have different locomotion devices: pseudopodia, flagella, and cilia. They can respond to stimuli due to photo-, chemo- and thermotaxis and other mechanisms.
- Under poor conditions, the parasitic protozoa turn into a cyst, i. e. they are covered with a dense capsule. In a cystic state, the life process stops.
Under favorable conditions, the cyst sheds its shell and turns into a vegetative form that continues an active life.
The detection of parasitic protozoa in material from a patient presents almost no difficulties. A Pap smear and an additional thick drop of blood are usually examined.
Stools are usually examined fresh using a heated table. To detect amoebic cysts, Lugol's solution is added to the stool, which stains the internal structures.
At this time, all protozoa are classified in the kingdom Protista, which includes seven species, of which only three are of medical importance.
Subphylum Sarcodae
Sarcodidae cell shape varies; the cell membrane forms protrusions that can then return to their original shape called pseudopodia.
Thanks to them, the cell moves. Sarcodidae live absolutely everywhere: soil, freshwater, seas. Infectious diseases caused by Sarcodidae are common throughout the world, but are more common in the tropics and subtropics.
Pathogenic amoeboid sarcoids most often affect the digestive system of humans, these are intestinal parasites. Free-living amoebae of other orders also cause serious infections when accidentally ingested and colonized in the human body.
Microscopic examination of feces is used to diagnose amebiasis. They contain vegetative or cystic forms of sarcoid. When examining stool preparations using a special heated table, it is possible to detect pseudopodia of amoebae and their forward movements.
For the treatment of amoebiasis, drugs are used, which are divided into groups: contact, which act on forms living in the intestinal lumen, and systemic tissue amoebicides, which act on amoebae that have penetrated the tissue of the intestine and other organs.
In addition to treatment, aspiration of the liver abscess is performed if chemotherapy is ineffective or there is a threat of rupture of the abscess. The table below describes the main parasitic protozoa of the subphylum Sarcodidae.
Subphylum Flagellates
Representatives of the flagellar subtype, in addition to the cytoplasmic membrane, have a pellicle (such a shell provides a permanent shape) and flagella (one or many).
The flagellum contains contractile fibrils that allow it to move. Some representatives of the flagellates have a wavy membrane inside which the flagellum/flagellum lies without going beyond its boundaries.
The flagellum starts from the kinetosome, which stores energy. Inside some flagellates is an axostyle - a thick cord inside the body that provides support.
The main symptoms and signs of infection by representatives of the flagellate subtype are presented in the table below.
| Representative/ Localizations | Symptoms | Diagnosis |
|---|---|---|
| Giardia (Lamblia intestinalis or Giardia lamblia) / duodenum and small intestine | Nausea, heartburn, abdominal pain, flatulence, heartburn, diarrhea, intoxication of the body, exhaustion | Microscopy of duodenal contents, stool examination, ELISA for Giardia antibodies |
| Intestinal trichomonas (Trichomonas hominis/intestinalis)/ Lower part of the small intestine, large intestine | Colitis, enterocolitis, cholecystitis, diarrhea | Detection of vegetative forms and cysts in the liquid feces of the patient |
| Trichomonas vaginalis (Trichomonas vaginalis) / Vagina, cervical canal, urethra - in women. Urethra, prostate, testicles - in men | Colpitis, urethritis in women, itching, burning in the genital area, foamy yellow discharge from the vagina. Asymptomatic carriage, urethritis, prostatitis in men | Vaginal discharge in women, urethral discharge and prostate secretion in men, PCR, culture |
| Oral trichomonas (Trichomonas tenax)/ Oral cavity, respiratory tract, tonsils, gums | Caries, periodontitis, ENT diseases | Fingerprints, culture |
| African trypanosomes (Trypanosoma brucei gambiense and Trypanosoma brucei rhodesiense)/ Skin at the site of penetration, neck and occiput lymph nodes, bloodstream | Fever attacks, painful lymph nodes, skin rash, headache, drowsiness, tremor of limbs, paralysis, slurred speech, coma, convulsions, exhaustion, acute heart failure, death | Examination of the bite site, lymph node biopsy. Thick drop method and blood smear, stained by Wright or Romanowski-Giemsa, examination of cerebrospinal fluid. Infection of laboratory animals, RSK, RIF, ELISA |
| American trypanosome (Trypanosoma cruzi)/ Blood | Swelling of the skin at the site of penetration, enlargement of the nearby lymph nodes, swelling of the eyelids, enlargement of the parotid lymph nodes. The acute form in newborns leads to heart and brain damage with a fatal outcome. Chronic form in adults, sick in childhood - arrhythmia, extrasystole, dilatation of the large intestine with hypertrophy of the wall, expansion of the esophagus, myxedema, paralysis | Microscopy of blood smears, biopsy samples from lymph nodes, spleen and other organs - for the acute form. Serological studies, xenodiagnostics (feeding uninfected bugs from the patient's body and detecting trypanosomes in their feces), infection of laboratory animals - for the chronic stage |
| Cutaneous leishmaniasis (Leishmania tropica)/Skin | Skin nodule, regional lymph node enlargement, nodule ulceration with "dry" or "wet" painless ulceration, daughter lesions, skin scar after healing | Microscopy of tissue from the bottom of the ulcer with staining according to Romanowski-Giemsa, RIF, RSK, ELISA |
| Mucosal leishmaniasis (Leishmania braziliensis) / Skin and mucous membranes | Skin nodules, enlarged regional lymph nodes, skin ulcers, scar formation. On the mucous membranes - painless deforming lesions of the mouth and nose, ulcers on the tongue, mucous membrane of the cheeks and nose, destruction of the nasal septum, hard palate, pharynx, fever, weight loss, addition of bacterial infections | Microscopy of discharge from ulcers, biopsy of damaged organs, RSK, RNGA |
| Visceral leishmaniasis (Leishmania donovani)/ Cells of the spleen, liver, bone marrow, lymph nodes | Enlarged liver, spleen, anemia, exhaustion, intoxication, intestinal bleeding, diarrhea, grayish spots on face and head, death | Detection in biopsy smears of spleen, lymph nodes, bone marrow, RIA, ELISA, RSK |
Disputants
Sporozoa have no locomotor organs. They consume nutrients throughout the body and often exhibit intracellular parasitism. Sporozoa include the causative agents of malaria and toxoplasma. Toxoplasmosis is more dangerous for pregnant women and people with proven immune deficiency (for example, against the background of HIV infection).
Pregnant women with toxoplasmosis are prescribed 3 million units of spiromycin three times a day, every day for fourteen to twenty days.
Parasitic cilia
Cilia do not change their body shape and have a pellicle. Motor maneuvers are performed due to the huge number of cilia covering the entire cell.
Cilia have two nuclei: a large one responsible for cellular metabolism and a small one that transmits hereditary information.
Cilia have an organized digestive system: the cytostome is the mouth of the cell, the cytopharynx is the pharynx of the cell. Digestive enzymes are gradually released from the vacuoles, which ensures complete absorption of nutrients. The undigested parts of the food come out through the dust, a special formation at the end of the body. The symptoms that can occur when these parasites are present in the intestines are presented in the table below.
| A pathogen | Localization | Symptoms | Diagnosis |
|---|---|---|---|
| Balantidium coli | Colon | Fever, intoxication, abdominal pain, diarrhea with mucus and blood, nausea, vomiting. Asymptomatic, carrying cysts | Detection in stool, colon biopsies |
Treatment of balantidiasis includes prescribing antibacterial and antiprotozoal drugs according to one of the following schemes.
General characteristics of helminths
Helminthology is the science of worms (helminths) that parasitize the body of other animals, the diseases they cause, as well as the methods of diagnosis, prevention and treatment.
The helminth fauna is the totality of all helminths identified in humans. Helminthic diseases, unlike diseases caused by protozoa (protozoa), are not common everywhere.
Most worms carry out their activity in the digestive tract of humans, others can attack parenchymal organs, blood and genitourinary system.
The spread of helminths depends on the labor activity of the population, the eating habits of the different population groups and the economic condition of the country. The most widespread in our country are the following helminthiasis.
Helminth diseases are divided into geohelminthoses and biohelminthoses. In order for geohelminth eggs or larvae to develop, they must be in the external environment to mature and acquire pathogenic properties. These are roundworms, whipworms, nekators, etc.
Biohelminths go through their life cycle with an alternate host, and in order to acquire pathogenic properties, their eggs must enter an intermediate and sometimes an additional host. These are cattle, pig tapeworm, opisthorchis, fasciola, etc.
The localization of parasitic worms or their larval forms in the human body is very diverse: in the small and large intestines (intestinal helminthiasis), bile ducts and liver, blood circulation, central nervous system and eyes, skin, muscles, etc. Intestinal parasites occur. in humans more often than tissue.
In the pathogenesis of helminthiasis, the occurrence of allergic reactions and a severe degenerative process are of great importance. They appear due to the large number of antigens that worms have.
Other factors of pathogenesis include the direct influence of enzymes that form larval forms and adults. In the later stages of development of worms, the mechanical factor and the direct traumatic effect of the fixing organs play an important role.
The diagnosis is usually confirmed by an interview, a clinical picture of the disease and the detection of eggs, larvae, fragments or adult worms in the feces, sputum and duodenal juice.
Serological reactions, X-ray and ultrasound examination also play an important role in the diagnosis of helminthiasis.
In general, about three hundred species of pathogenic worms have been found in humans, twenty-eight species of which are the most common: 12 species of trematodes, 8 species of cestodes, 8 species of nematodes.